Thursday, 16 April 2020

An exciting new polymetallic mineral deposit found in West Cornwall

Today would have seen the first of our summer Cornish Mining Sundowners at Falmouth's Chain Locker, which now lies deserted due to the Coronavirus lockdown.
I am sure that the conversation would have centred on the announcement by Canadian company Strongbow, the company behind the planned reopening of South Crofty tin mine, of another significant new discovery of high grade copper and tin at Strongbow’s United Downs exploration project. 
Strongbow completed the acquisition of the South Crofty mine plus additional mineral rights located in Cornwall in July 2016 and some of these mineral rights cover old mines that were historically worked for copper, tin, zinc, and tungsten. United Downs is located approximately five miles east of South Crofty and lies within the densely mined Gwennap district, which was the richest copper producing region in  the world in the 18th and early 19th centuries, and was referred to as “the richest square mile on earth” (MEI Blog 27 October 2018).
The Gwennap mining area today
Strongbow and local company Cornish Lithium have a mutually beneficial agreement to explore each other’s mineral rights. Cornish Lithium has the right to explore Strongbow’s mineral rights in Cornwall for lithium in brine occurrences while Strongbow retains the rights to any hard rock mineralisation.
In 2019 Cornish Lithium started to conduct diamond drill testing for lithium in brine at United Downs and the new discovery was made by Cornish Lithium who intersected semi-massive sulphide mineralisation between 90.6 and 105m depth, assaying 7.46% Cu, 1.19% Sn, and 0.15% Zn.
The mineralisation is of similar nature to that mined at Wheal Jane and Mount Wellington mines, located 1.5km to the east; and copper grades reflect recorded historical mine production from United Mines located approximately 200m to the south. All of the mineralisation exploited historically is related to either quartz veins or quartz-tourmaline veins hosted within “killas”, the local name for metasedimentary rocks that overlie granite intrusions.
The Wheal Jane mine was discovered and developed into a modern mine in the late 1960s, initially by Consolidated Goldfields, and thereafter by Rio Tinto Zinc.  Mining activities at Wheal Jane and Mount Wellington ceased in early 1991, due largely to the Tin Crisis of 1985, but processing of South Crofty ore continued until March 1998 when ongoing low tin prices forced its eventual closure.
As drilling proceeds we will no doubt learn of the extent of this deposit and whether it is large enough to have ore-body potential. Hopefully there will be more news at next month's 'virtual sundowner'.


  1. So nice to get some positive news,Barry. I am glad mining companies are joining together, share their knowledge, extract every element present and still keep their identity and ownership.
    The p\practices they would adopt, both for mining and recovery of minerals/metals would of great interest.

  2. I'm intrigued with this one, when plotted, the strike of this runs through United Downs industrial, just North of the two GEL boreholes and about 20m South of the most southerly point of the Wheal Maid decline. So GEL missed this by about 10m and Rio Tinto by 20m (30m) total, and the liberalisation width is as much as 16m - that's pretty unlucky by anyone's standards!

  3. The above comment(from unknown) is very interesting. Though I am not a Mining Engineer, I am keen to understand that comment--does it imply that selection of borehole sites was not proper andor/proper chemical analyses was not done on core samples to interpret data to get an indication.
    May ignore my comment if not put in proper mining terminology.

  4. No not at all, the assaying will be spot on. There just isn't the data at present to know what it is. Is it a lode or is it a very localised area of mineralisation.

  5. Thank you, Sir for giving the reply. Yes made it so clear to me on how to get proper resource and reserve estimates.
    I am sure such kind of exchanges of views not only help professionals and serve (as I feel) the purpose of Barry's efforts in running these Blogs with so much information.
    I hope many more take active interest and benefit others in the profession.

  6. From copious diary entries and notes I found the Wheal Jane geologists gave me lode material from the Whiteworks underground and I diluted it down with development waste to give a more realistic grade for test work. I basically had a standard lab WJ procedure, grind, sulphide float, gravity, regrind and tin flotation stage. The lode was 3.9%Sn, 2.2 % Cu and no Zn, diluted down to give the test work 1.5% Sn, 1% Cu. The cassiterite was coarse, the copper predominately chalcocite with minor chalcopyrite. Gravity wise the tin jumped out and the copper had an 88% flotation recovery to a 36% Cu concentrate and 350 ppm Ag. Comments on variations in head grades for the various samples pointed to erratic mineralization. I suspect if Strongbow have anything there, it’ll be a breeze!
    Cheers, Stephen Young, Canada


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